Various techniques are known for treating oil and gas formations or strata with fluorides, acids, fracturing, flushing fluid, proppants, stimulating chemicals, and other treatments to enhance recovery of hydrocarbons or other formation fluids. Such methods would include pumping directly down the casing with perforations in the casing adjacent to desired strata of the subterranean structure. Tools for injecting treating fluids of various types which may include dispersed solids or gel generally include a pair of axially spaced packers between which the treating fluids are injected through perforation in a casing or directly into exposed hydrocarbon bearing strata. Some tools use several axially spaced swabs defining several annular spaces between the tool body and perforated areas of the casing with perhaps two concentric tubes supplying the same or different treatment solutions in each of the annular spaces for injection into the formation. U.S. Pat. No. 6,260,622 B1 describes such a tool.
Other techniques include a tool having an inlet from the casing and a tube extending downward within the production string for injecting flushing fluid into the production string just below the perforations in the casing during production. This particular arrangement requires an injection valve insert assembly as described in U.S. Pat. No. 5,718,289 granted Schnalzmeyer.
With advances in drilling technology, it is currently possible to drill horizontal wellbores deep into hydrocarbon strata or reservoirs. Utilization of horizontal wellbores allows extended contact with a reservoir or producing formation, thereby facilitating drainage and production from the reservoir. It is often necessary to hydraulically fracture or stimulate the reservoir through which the horizontal wellbore has penetrated.
Although horizontal wellbores allow more contact with the producing formation, some difficulties are encountered when horizontal wellbores are utilized which are not commonly experienced when vertical wells are used. Methods utilized in producing hydrocarbons from a formation or reservoir via vertical wells often proves to be inefficient when attempting to remove hydrocarbons from a reservoir where horizontal wellbores are drilled.
Jennings, Jr., in U.S. Pat. No. 4,951,751, describes a method of staging a fracturing treatment in horizontal wellbores where solidified gel is utilized as a diverting medium. As described, a horizontal wellbore is perforated at the end furthest from the angle of deviation from vertical of the wellbore so as to allow fluid communication with a desired interval of a formation. Once the desired perforations have been placed into the furthest end of the wellbore, a hydraulic fracturing operation is conducted through said perforations so as to fracture the desired interval of the formation. Thereafter, a solidifiable gel containing a gel breaker is injected into the wellbore where the perforations are made. Afterwards, a wiper plug is injected into the formation thereby displacing the gel to an area adjacent to the fractured interval. The solidifiable gel is allowed to form a solid gel in the formation adjacent to the perforations and a solid gel plug in the wellbore.
After the desired number of perforations have been placed into the wellbore so as to allow fluid communication with another interval of the formation closer to the angle of deviation from vertical and adjacent to said first interval, hydraulic fracturing is initiated so as to fracture a second desired interval of a formation. This activity is repeated as appropriate for the formation, then the gel breakers cause the solid gel in the formation and the gel plug to liquefy, after which injection pressure is applied so the wiper plugs are pumped out the perforations of the wellbore.
One of the problems in treating horizontal wellbores is getting a substantial volume of treating solutions in the appropriate region of the formation under pressure. Thus, it is necessary to pump the solutions at a high rate of volume (gal/min). Coiled tubing is used in some cases, U.S. Pat. Nos. 5,507,342, and 5,884,701 for example, for delivering treating solutions into formations. However, coil tubing come in specific length and when positioned in a formation for treatment, the treating fluid must be pumped through the entire length of the coiled tubing resulting in considerable friction and decrease in flow rate, although, while pumping, the coiled tubing may be reciprocated in the formation especially, horizontal boreholes in hydrocarbon bearing strata.
For treating extensive strata exposed to horizontal borehole conventional jointed tubing requires treating the furthest end of the deviated horizontal borehole from the vertical borehole. In order to accomplish such borehole treatment by connecting the treating solution pumping unit to a working string at the wellhead after the joints are run in the borehole to the end of the horizontal borehole with the treating solution dispersing tool at the end of the working string. Next the treating solution is pumped down the working string at the appropriate pressure and rate while the working string is being withdrawn from the borehole. After the first joint of tubing is pulled, the pumping of treating solution is stopped, the connection to the working string is uncoupled, and the pipe joint uncoupled from the working string. Then, the pumping unit must be reconnected and resume pumping treating solution down the working string and into the formation while the next pipe joint is being pulled and then stopping the treating operation to uncouple the pipe joint from the working string. The foregoing procedure is repeated until treatment of the borehole is complete. The foregoing procedure is time consuming and inefficient.
It should be apparent that a simpler and more efficient arrangement is needed to effectively treat strata or formations penetrated by horizontally deviated boreholes from the vertical.